Outdoing the best spy fiction, former CIA inspector general Waller (Beyond the Khyber Pass, 1990, etc.) tells a series of riveting stories about the hidden war between the Germans and the Allies in WW II. From the beginning, the intelligence war was a central element of the conflict. Waller relates some well-known stories, like the breaking of the British naval fleet codes by the Germans, which contributed to the great success of the Nazi U-boat effort, and the similar breaking of the German Enigma enciphering machine by Allied intelligence, which allowed the British to anticipate German strategy on the continent. He also offers speculations on the intelligence background of WW II riddles like the Hess flight to Scotland and the assassination of Reinhold Heydrich, one of the most violent and ambitious members of Himmler's inner circle. However, Waller also travels some less familiar ground, particularly in his detailed profile of Admiral Wilhelm Canaris, the brilliant, enigmatic head of the Abwehr, the military intelligence unit of the German Ministry of War. Canaris despised Nazism, secretly assisted the Allied war effort, and ultimately participated in the doomed 1944 attempt to assassinate Hitler. Waller also describes Operation X, which used Pius XII, an old friend of Canaris's, to help relay messages from the German Resistance movement to British intelligence; the ``Venlo incident'' in 1939, which cost Britain virtually its entire intelligence network on the continent; Allen Dulles's secret work as a ``special representative'' of FDR in Switzerland; and the intelligence intrigues surrounding the implementation of Hitler's invasion of France and his plan to invade the Soviet Union. More than a deft account of some some intriguing spy stories, Waller's history reminds us how crucial intelligence operations were to the war in Europe and to the Allies' ultimate success.